Magnetic recording media, such as disks are widely used for storing data. In order to write to or read form such recording media, storage devices such as disk drives are typically used. Storage devices typically include heads for reading from and/or writing to the recording media. A head is typically attached to a slider, which holds the head above the recording media. The slider is attached to a suspension, which supports the slider above the recording media. The slider is coupled to an actuator arm which moves the head, slider, and suspension across the recording media.
Currently magnetoresistive (MR) heads are increasingly popular for use in read heads. A MR head includes a MR sensor, which has a resistance that varies with an applied magnetic field. The MR sensor may be an anisotropic magnetoresistance (AMR) sensor or a giant magnetoresistance (GMR) sensor. In order to use the MR sensor, The MR sensor is coupled with electronics, which drive the MR sensor and read the signal from the MR sensor. The electronics are coupled with the MR sensor using a wire interconnect.
The signal from the MR sensor can be read by sensing the voltage across the MR sensor. In order to do so, a conventional voltage-sensing preamplifier (conventional VS preamplifier) is used. Typically, an input of the conventional VS preamplifier is coupled with the interconnect. Voltage from the interconnect is provided to input devices in the conventional VS and amplified by a gain stage in the conventional VS. The input devices typically include transistors. The amplified signal is then provided either as a single ended or differential signal to the remainder of the electronics.
Although the combination of the MR sensor, the interconnect, and the conventional VS preamplifier is capable of reading data on recording media, one of ordinary skill in the art will readily recognize that the ability of the storage device to read at higher data rates is limited. Previously, limitations in the bandwidth of the storage device were due to other portions of the electronics. However, improvements in other portions of the electronics have increased the bandwidths of these components of the storage device. As a result, the bandwidth for the storage device has increased. As the data rate increased, the interface between the MR sensor, the interconnect, and the conventional VS preamplifier has become of increasing importance in constraining the bandwidth of the storage device. In particular, the useful bandwidth of the conventional VS preamplifier as used in the storage device is limited. Thus, the ability of the storage device to read at higher data rates is also limited.
Conventional methods for addressing the limited bandwidth of the conventional VS preamplifier also have drawbacks. One reason for the limited bandwidth of the conventional VS preamplifier is the impedance mismatch between the MR sensor, a characteristic impedance of the interconnect, and the input impedance of the conventional VS preamplifier. The MR sensor has a resistance which can vary on the order of two or three to one. The interconnect typically has a relatively low characteristic impedance, generally on the order of fifty ohms. The characteristic impedance of the interconnect also changes. Different heads may be used in the storage device. These heads occupy different positions within the storage device. In order to reach these heads, the interconnects may have different lengths or shapes. Furthermore, the interconnect typically twists and bends during use, thereby changing the characteristic impedance of the interconnect. The conventional VS preamplifier has a very high input impedance, much more than the characteristic impedance of the interconnect. Thus, the input impedance of the conventional VS preamplifier does not match the characteristic impedance of the interconnect.
In the conventional VS preamplifiers the mismatch between the impedances of MR sensor, the characteristic impedance of the interconnect, and the input of the conventional VS preamplifier is partially addressed by providing a resistor coupled with input devices of the conventional VS preamplifier. The resistor is coupled in parallel with the bases of the transistors used as the input devices. This lowers the input impedance of the conventional VS preamplifier. However, one of ordinary skill in the art will readily recognize that the resistor causes increased signal attenuation, which is undesirable. Consequently, such a method may not be desirable in the conventional VS preamplifier.
Accordingly, what is needed is a system and method for improving the bandwidth of the conventional VS preamplifier and, therefore, the data rate for the storage device. The present invention addresses such a need.